Proas are strange

proa foils

The question of foil location on (atlantic) proas seems wide open.

Fin(s) may be single or multiple, on lee or center of vaka, on crossbeams or even on ama. Any opinion about locating a (reversible) foil on the ama?

Rudders - vaka ends, quarter hung, etc. Clearly, (I think) a rudder midships wouldn't work.

What about foils with trim tabs?

What about using the new fwd rudder as trim tab?

Then of course is the Deep V vs foil conversation. Clearly a deep V is more wetted area, but then, long thin vakas and amas already have a lot of wetted surface, compared to a sphere. But they have minimal cross section to push through the water.

My question here is how much of the conventional wisdom regarding these matters is the way it is due to the need to tack through the eye of the wind.

Glad to see discussion on these questions.

 

Hi Anatol.
1. I wrote that it's impossible for a proa to shunt as fast as a bermuda rigged mono tacks, just because, the mono keeps moving through the eye of the wind. The proa must stop and get going again..... what ever you do, you lost too much time...

Crystal Clear is the smallest blue water pacific proa in the world, therefor all she has is 70 liters water capacity, all water will be in large plastic mineral water bottles. we will move the water bottle by bottle. But, what, how and when, depends very much on conditions and heading.....

I've been filming her since I began, all films are on my youtube channel.

All d best brother, proas are just cool!

 

Hi Anatol,

Good luck with your design, anyway I think that a good design is a balance between all of your goals and purposes that you want the boat for. Make a clear definition what you want your boat to do and start from there. What you want is to minimize the disadvantages and maximize the advantages. But, on your boat, only you know how to do that............

All d best brother, and yea when you got more info, bring it on.
rael

 

I had a good scoff at this suggestion when I first read it but after thinking about it am wondering if it could actually function.

Given that the pivot point of the vaka is likely to 1/4 to 1/3 of the length measured from the stem then there may be enough of a lever for a midships (in the fore-and-aft sense) rudder to work, at least once the boat is moving and is generating some side force. My gut feeling is that it would have to be quite a small foil to prevent it dominating the centre of lateral resistance all by itself.

Since proas often have a tendency to sail slightly trimmed by the bow this would also help, especially if you had a fairly deep entry like a Samoan canoe or some of the ethnic Wharram designs (e.g. Melanesia, Tahiti Wayfarer etc.).

Might be better suited to a Pacific rather than an Atlantic proa though?

 

I've learned I'm more ready to query conventional wisdom than most. Proa design is a fascinating exercise for me because proas are so radically different to conventional monos or even multis that I think ideas that are 'common-sense' in conventional design just may not apply in proas. The challenge is to logically or empirically determine which aspects of conventional design apply, and which don't. Fun fun fun!

 

Interesting point. Since my ply models involve long rectangular sheet that come to fine vertical bows, I get foil-like bows for free. But the fine stern would tend to diminish the effect, right? (I do get some significant rocker in my design though)

If the Vaka tracks like it was on rails (and the Ama was say, cylindrical) - how about a rudder midships on the Ama? See- I'm up for considering any crazy idea

 

I can imagine that a midships rudder might have some degree of functionality but I am struggling to think how it might actually be a good idea? I can only really come up with the simplicity of one foil instead of 2.

If you are interested in how foils placed in various locations might work then perhaps there is something to be learned from from Chinese bamboo sailing rafts that used 6 or more daggerboards, paddles and steering oars in various configurations? Information (in English at least) seems a little hard to come by but there may be some insights?

 

that sounds right. But one of the things I've come to understand about proas is that a lot of things are rotated 90deg, wrt conventional boats, so I thought, what happens if the rudder is way out on the ama, would it drive the vaka around the centerline of the vaka - or around the axis of a single foil midships or lee gunwale midships...

I've heard also of some pacific craft with multiple daggerboards, or multiple slots...great for incremental trim, not so good for close quarters maneurverability

 

Godiva Chocolatier might be a good reference point from which to start.
http://www.wingo.com/newick/godiva/

 

Great link - I'd heard of it but hadn't looked closely - thanks!